Sleeve for die casting shot tube

ABSTRACT

A shot tube for the introduction of molten metal into a die cavity has a casing with a first end, a second end and a bore extending through the casing. The first end is adapted to be connected to the die cavity and a sleeve protrudes from the second end of the casing. The sleeve has a pour opening for the introduction of molten metal. A hard lubricious coating may also be applied to the interior surface of the shot tube to reduce sticking of cooled metal within the shot tube. A method for producing the shot tube described above is also disclosed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to die casting using a shot tube and, more particularly, relates to a sleeve which is part of the shot tube.

2. Description of the Related Art

Die casting operations typically involve the use of a shot tube to introduce molten metal into a die cavity under high pressures. In general, the shot tube is an open pipe with a large hole through the wall on one end to allow for the introduction of molten metal from a ladle. Once inside the shot tube, the molten metal is quickly pushed, or shot, into the die cavity using a piston, which closely fits with the inside diameter of the shot tube. The shot tube is typically made from a high-quality tool steel, such as H13, that is heat treated to a high initial hardness to resist the abrasion and erosion from the molten metal being poured into the tube and pushed axially along the tube.

Failure of the shot tube is generally caused by excessive erosion and hot corrosion below the pour hole due to the molten metal impacting upon the bottom of the shot tube during the pouring process. The molten metal produces a thermal shock event which can cause high thermal gradients through the wall of the shot tube, causing corrosive attack and cracking near the surface that results in pieces being carried out by the molten metal as the molten metal is forced down the shot tube. Further abrasion and erosion then occurs as this molten metal is pushed through the tube. The resulting crater at the bottom inside diameter of the tube allows the molten metal to blow back behind the piston during future cycle pressurization. The resulting loss of molten metal volume can cause die fill problems, resulting in poor quality cast parts. This erosion can fail a shot tube in as little as three weeks of operation, resulting in machine down time to replace and repair the shot tube. The chilled metal also presents problems for the operation of the piston. Typically, a lubricant must be introduced to allow for less drag between the piston and the tube, especially as the piston face expands due to the contact temperature while the shot tube tends to distort as most of the thermal energy is initially concentrated along the bottom portion of the tube as the molten metal is poured. Cleaning out the tube after several runs to clear the leftover chilled metal and used lubricants also slows the process efficiency.

U.S. Pat. No. 4,733,715, which is hereby incorporated by reference, is directed to a shot tube, whereby the entire shot tube is lined with a cemented carbide sleeve. While the design utilizing cemented carbide for a sleeve offers prolonged life when compared to a sleeve made from high-quality tool steel, when any part of the shot tube is excessively worn, it is necessary to replace the entire shot tube. Additionally, although cemented carbide is more tolerant to thermal shock, the difference of the coefficient of thermal expansion between cemented carbide and high-speed tool steel is significant and, as a result, significant thermal stresses are developed at the junction of the cemented carbide sleeve and the high-speed tool casing, especially in the region of the pour hole.

A design is needed which extends the life of the shot tube and/or simplifies the ease of replacing a damaged portion of the shot tube.

Additionally, cemented carbide is a fairly expensive material and, as a result, a design which most efficiently utilizes cemented carbide within a shot tube is desired to minimize the overall cost of the shot tube and, at the same time, provide increased life to the shot tube.

Furthermore, with each cycle of the shot tube, a layer of molten metal tends to cool and accumulate along the wall of the shot tube. This accumulation of chilled metal sticks to the shot tube wall and not only may interrupt the piston/plunger motion, but also may create an undesirable gap between the piston/plunger and the shot tube wall. A design is needed to reduce this build-up of chilled metal on the wall of the shot tube.

SUMMARY OF THE INVENTION

In one embodiment, a shot tube for the introduction of molten metal into a die cavity has a casing with a first end, a second end and a bore extending therethrough. The first end is adapted to be connected to the die cavity. A sleeve protrudes from the second end of the casing and has a pour opening for the introduction of molten metal.

In another embodiment, a shot tube for the introduction of molten metal into a die cavity has a casing with a first end, a second end, a bore extending therethrough. The casing has a casing wall defining an interior surface with a profile and the first end is adapted to be connected to the die cavity. A forward section with a pour opening extends through the casing wall for the introduction of molten metal into the casing. The interior surface has a recess extending therein positioned diametrically opposite to the pour opening. The recess extends within the interior surface of the casing. A protective insert having a shape of the recess is placed within and fills the recess such that the profile of the interior surface will be uninterrupted along the bore within the casing.

Another embodiment of the subject invention is directed to a method of manufacturing a shot tube for the introduction of molten metal into a die cavity. A casing is produced having a first end, a second end and a bore extending therethrough. The first end is adapted to be connected to the die cavity. A sleeve is secured within the casing so that the sleeve protrudes from the second end of the casing. The sleeve has a pour opening outside of the casing for the introduction of molten metal and the sleeve is made of cemented carbide.

In yet another embodiment of the subject invention, a lubricious coating is applied to the wall of the shot tube to prevent chilled metal from sticking to the shot tube wall.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

Further features of the present invention, as well as the advantages derived therefrom, will become clear from the following detailed description made with reference to the drawings in which:

FIG. 1 illustrates a sectional view of a shot tube in accordance with a first embodiment of the subject invention;

FIG. 2 illustrates a sectional view of a shot tube in accordance with a second embodiment of the subject invention;

FIG. 3 illustrates a sectional view of a shot tube in accordance with a third embodiment of the subject invention;

FIG. 4 illustrates a sectional view of a shot tube in accordance with a fourth embodiment of the subject invention;

FIG. 5 is a perspective view of the sectional view illustrated in FIG. 4;

FIG. 6 is a sectional view of a shot tube in accordance with a fifth embodiment of the subject invention;

FIG. 7 is a sectional view of a shot tube in accordance with a sixth embodiment of the subject invention; and

FIG. 8 is a sectional view illustrating a permanent hard surface coating that may be applied to the wall of any of the shot tubes heretofore described.

DETAILED DESCRIPTION OF THE INVENTION

Directing attention to FIG. 1, a shot tube 10 is used for the introduction of molten metal into a die cavity 12. The shot tube 10 has a casing 15 with a first end 17, a second end 19 and a bore 25 extending through the casing 15. The first end 17 is adapted to be connected to the die cavity 12. The shot tube 10 further includes a sleeve 30 protruding from the second end 19 of the casing 15. The sleeve 30 has a pour opening 35 for the introduction of molten metal. As illustrated in the embodiment of FIG. 1, not only does the sleeve 30 protrude from the second end 19, but additionally extends within and along the length of the casing 15. However, the pour opening 35 is in a portion of the sleeve 30 outside of the casing 15. As a result, the sleeve 30 in the region below the pour opening, where the sleeve 30 is exposed to the greatest thermal shock, does not experience additional thermal stress caused by the difference in coefficient of expansions between the sleeve 30 and the casing 15. To further reduce the thermal stress between the sleeve 30 and the casing 15, the casing 15 has a casing outer diameter DC and the casing 15 tapers so that the casing outer diameter DC reduces in the region of the second end 19. Additionally, the sleeve 30 has a sleeve outer diameter DS and the casing outer diameter DC proximate to the second end 19 may reduce continuously until the casing outer diameter DC is approximately equal to the sleeve outer diameter DS as illustrated in FIG. 1.

A portion 40 of the sleeve 30 may extend from the casing 15 a distance L of up to five times the outer diameter DC of the casing 15.

In a preferred embodiment, the sleeve 30 is made of cemented carbide, such as tungsten carbide, titanium carbide, tantalum carbide, chromium carbide, niobium carbide or silicon carbide. The sleeve 30 may also be made up of a ceramic based material, such as silicon nitride, alumina, SiAion, boron carbide, titanium diboride, zirconia or aluminum nitride.

FIG. 2 illustrates a second embodiment of the subject invention wherein the portion 40 of the sleeve 30 protrudes from the second end 19 of the casing 15 and is removably secured to the second end 19 of the casing 15. That portion 40 of the sleeve 30 may be mechanically secured to the second end 19 of the casing 15 using techniques known to one of ordinary skill in the art of die casting. Under such circumstances, it may be desirable to include a seal 45 between the second end 19 of the casing 15 and the portion 40 of the sleeve 30.

In a third embodiment illustrated in FIG. 3, the shot tube 10 is similar to the embodiment illustrated with respect to FIG. 2, but the sleeve 30 begins at a location proximate to the second end 19 of the casing 15 and extends away from the casing 15. Under these circumstances, the sleeve 30 is again essentially isolated from the casing 15 and, as a result, the thermal shock imparted to the sleeve 30 from the pouring of the molten metal within the pour opening is isolated. Therefore, the opportunity for thermal stress based upon the difference in coefficient of thermal expansions between the casing 15 and the sleeve 30 is minimized. Once again however, the sleeve 30 may be mechanically secured to the second end 19 of the casing 15 and a seal 45 may be included between the sleeve 30 and the second end 19 of the casing 15.

What has been discussed so far is the sleeve 30 in the shape of a cylinder extending from the casing 15. The sleeve 30 may be attached directly to the second end 19 of the casing 15 or may extend the entire length of the casing 15.

In order to minimize the expense of materials used to protect the casing 15 and also to minimize the manufacturing, in a fourth embodiment of the subject invention illustrated in FIG. 4 and FIG. 5, the shot tube 10 has a casing 15 with a first end 17, a second end 19 and a bore 25 extending through the casing 15. The first end 17 is adapted to be connected to a die cavity 12. The casing 15 has a forward section 60 with a pour opening 35 extending through a casing wall 62 for the introduction of molten metal into the casing 15. The casing wall 62 defines an interior surface 65 with a recess 70 extending therein. The recess 70 is positioned diametrically opposite to the pour opening 35 and extends within the interior surface 65 no higher than a point 75 midway up the interior surface 65 of the casing 15. A protective insert 80 having a shape of the recess 70 is placed within and fills the recess 70. As a result, the profile of the interior surface 65 will be uninterrupted along the length of the bore 25 within the casing 15. The protective insert 80 may be secured within the recess 70 through shrink fitting or any other conventional means known to those skilled in the art of using cemented carbide in metalworking applications. In a preferred embodiment, the protective insert 80 may be made of cemented carbide and, in particular, tungsten carbide, titanium carbide, tantalum carbide, chromium carbide, niobium carbide or silicon carbide. In another embodiment, the protective insert 80 may be made from ceramic-based materials, such as silicon nitride, alumina, SiAion, boron carbide, titanium diboride, zirconia or aluminum nitride.

Even though the protective insert 80 is mounted within the casing 15, in yet another embodiment illustrated in FIG. 6, a forward section 85 of the casing 15 may be removably secured to the remainder of the casing 15. In particular, the forward section 85 may be mechanically secured to the remainder of the casing 15. Under such circumstances, it may be desirable to include a seal 45 between the forward section 85 of the casing 15 and the remainder of the casing 15. The forward section 85 has a recess 70 and a protective insert 80 therein in a fashion similar to that already described in conjunction with FIGS. 4 and 5.

As illustrated in FIG. 7 and in contrast to the protective insert 80 shown in FIG. 6, a recess 90 may extend all of the way around the interior surface 65, such that a protective insert 95 has a cylindrical shape.

A method of manufacturing a shot tube for the introduction of molten metal into a die cavity is possible by producing a casing 15 having a first end 17, a second end 19 and a bore 25 extending through the casing 15. The first end 17 is adapted to be connected to a die cavity 12. A sleeve 30 is secured to the casing 15 so that the sleeve 30 protrudes from the second end 19 of the casing 15. The sleeve 30, which is made of a hard material such as cemented carbide, has a pour opening 35 outside of the casing 15 for the introduction of molten metal.

Over time, chilled metal from the pouring of molten metal into the shot tube tends to stick and cumulate on the wall of the shot tube. Directing attention to FIG. 8, to minimize this occurrence, a permanent hard surface coating 100 may be added to the interior surface 65 of the assembled shot tube 10 to enhance the survival of the tube and the piston/plunger and to greatly eliminate the need for cleanout and the addition of temporary lubricants into the process. Such a coating may be applied on the inside surface of the tube using chemical vapor deposition or thermal spray techniques using hard and lubricious compositions, such as titanium carbide, titanium nitride, titanium carbo-nitride, titanium diboride, molybdenum disulphide or diamond and diamond-like materials.

Even though these coatings are typically very thin layers, the surfaces can be multiple layer coated to increase the adhesion properties and the overall life. Such a coating may be applied to the interior surface 65 of the bore 25 along part of or the entire length of the bore 25. As illustrated in FIG. 8, the sleeve 30 has an interior surface 65 that is coated. Although all of the interior surface 65 is coated, it is possible to coat only a portion of the interior surface 65. It is also possible and easy to envision that when a portion of the bore 25 is occupied by the sleeve 30 or a protective insert 80 (FIGS. 6-7), all or part of the casing interior surface may be coated.

In each of the embodiments discussed herein, the pour tube bore is cylindrical. The additional stiffness provided by a hard metal sleeve/insert maintains a more round cross section, thereby minimizing warpage and improving the seal of pistons/plungers for use with vacuum-assisted die casting operations.

A prototype comprised of a solid one-piece liner of tungsten carbide/cobalt was shrunk-fit into the bore of a steel shot tube made from H13 steel. This prototype was used in a production aluminum die casting operation for a total of at least 10,000 shots. Upon examination of the carbide liner, it was noted to have no visible wear in the proximity of the molten aluminum pore hole nor anywhere downstream. It should be noted as a matter of experience, a shot tube made of H13 steel, without a carbide liner, would have shown a very large and deep scar clearly visible to the eye after 10,000 shots.

While the invention has been specifically described in connection with certain specific embodiments thereof, it is to be understood that this is by way of illustration and not of limitation, and the scope of the appended claims should be construed as broadly as the prior art will permit. 

1. A shot tube for the introduction of molten metal into a die cavity, where the tube is comprised of: a) a casing having a first end, a second end and a bore extending therethrough, wherein the first end is adapted to be connected to the die cavity; b) a sleeve protruding from the second end of the casing, wherein the sleeve has a pour opening for the introduction of molten metal and wherein the pour opening is proximate to the second end of the casing; and c) wherein the sleeve is made of a material from the group consisting of cemented carbide and ceramic.
 2. The shot tube in accordance with claim 1, wherein the sleeve additionally extends within and along the length of the casing.
 3. The shot tube in accordance with claim 2, wherein the portion of the sleeve protruding from the second end of the casing is removably secured to the second end of the casing.
 4. The shot tube in accordance with claim 3, wherein the sleeve is mechanically secured to the second end of the casing.
 5. The shot tube in accordance with claim 2, wherein the casing has a casing outer diameter and wherein the casing tapers so the casing outer diameter reduces in the region of the second end.
 6. The shot tube in accordance with claim 5, wherein the sleeve has a sleeve outer diameter and the casing outer diameter proximate to the second end reduces continuously until the casing outer diameter is approximately equal to the sleeve outer diameter.
 7. The shot tube in accordance with claim 1, wherein the sleeve begins at a location proximate to the second end of the casing and extends away from the casing.
 8. The shot tube in accordance with claim 7, wherein the portion of the sleeve protruding from the second end of the casing is removably secured to the second end of the casing.
 9. The shot tube in accordance with claim 8, wherein the sleeve is mechanically secured to the second end of the casing.
 10. The shot tube in accordance with claim 1, wherein the sleeve extends from the casing a distance of up to five times the casing outer diameter.
 11. The shot tube in accordance with claim 1, wherein the sleeve is made of cemented carbide.
 12. The shot tube in accordance with claim 11, wherein the cemented carbide is one from the group consisting of tungsten carbide, titanium carbide, tantalum carbide, chromium carbide, niobium carbide, and silicon carbide.
 13. The shot tube in accordance with claim 1, wherein the sleeve is made of a ceramic material.
 14. The shot tube in accordance with claim 13, wherein the ceramic material is one from the group consisting of silicon nitride, alumina, SiAion, boron carbide, titanium diboride, zirconia, and aluminum nitride.
 15. The shot tube in accordance with claim 1, further including a lubricious coating applied to the interior surface of the bore.
 16. The shot tube in accordance with claim 15, wherein the lubricious coating is one from the group consisting of titanium carbide, titanium nitride, titanium carbo-nitride, titanium diboride, molybdenum disulfide, diamond materials and synthetic diamond materials.
 17. A shot tube for the introduction of molten metal into a die cavity, where the tube is comprised of: a) a casing having a first end, a second end and a bore extending therethrough, wherein the first end is adapted to be connected to the die cavity; and b) a sleeve protruding from the second end of the casing, wherein the sleeve has a pour opening for the introduction of molten metal; wherein the sleeve begins at a location proximate to the second end of the casing and extends away from the casing; wherein the sleeve is removably secured to the second end of the casing; and wherein the sleeve is made entirely of cemented carbide.
 18. A shot tube for the introduction of molten metal into a die cavity, where the tube is comprised of: a) a casing having: i) a first end, a second end, a bore extending therethrough, and a casing wall defining an interior surface with a profile, wherein the first end is adapted to be connected to the die cavity; and ii) a forward section with a pour opening extending through the casing wall for the introduction of molten metal into the casing, wherein the interior surface has a recess extending therein, wherein the recess is positioned diametrically opposite to the pour opening and extends within the interior surface no higher than midway up the interior surface of the casing; and b) a protective insert having a shape of the recess such that the insert may be placed within and fills the recess such that the profile of the interior surface will be uninterrupted along the bore within the casing.
 19. The shot tube in accordance with claim 18, wherein the protective insert is made of cemented carbide.
 20. The shot tube in accordance with claim 19, wherein the cemented carbide is from one of the group consisting of tungsten carbide, titanium carbide, tantalum carbide, chromium carbide, niobium carbide, and silicon carbide.
 21. The shot tube in accordance with claim 1, wherein the sleeve is made of a ceramic material.
 22. The shot tube in accordance with claim 21, wherein the ceramic material is one from the group consisting of silicon nitride, alumina, SiAion, boron carbide, titanium diboride, zirconia, and aluminum nitride.
 23. The shot tube in accordance with claim 18, wherein the forward section of the casing is removably secured to the remainder of the casing.
 24. The shot tube in accordance with claim 24, wherein the forward section is mechanically secured to the remainder of the casing.
 25. The shot tube in accordance with claim 18, wherein the recess extends around the entire interior surface.
 26. The shot tube in accordance with claim 18, further including a lubricious coating applied to the interior surface of the bore.
 27. The shot tube in accordance with claim 26, wherein the lubricious coating is one from the group consisting of titanium carbide, titanium nitride, titanium carbo-nitride, titanium diboride, molybdenum disulfide, diamond materials and synthetic diamond materials.
 28. A method of manufacturing a shot tube for the introduction of molten metal into a die cavity, comprising the steps of: a) producing a casing having a first end, a second end and a bore extending therethrough, wherein the first end is adapted to be connected to the die cavity; and b) securing a sleeve within the casing so that the sleeve protrudes from the second end of the casing, wherein the sleeve has a pour opening outside of the casing for the introduction of molten metal, wherein the pour opening is proximate to the second end of the sleeve, and wherein the sleeve is made of cemented carbide.
 29. The method in accordance with claim 28, further including the step of depositing upon the interior surface a layer of a lubricious coating.
 30. A shot tube for the introduction of molten metal into a die cavity, where the tube is comprised of: a) a casing having a first end, a second end and a bore extending therethrough, wherein the first end is adapted to be connected to the die cavity; and b) a sleeve protruding from the second end of the casing, wherein the sleeve has a wall with a pour opening for the introduction of molten metal, wherein when viewed from the side, the depth of the pour opening is approximately equal to the thickness of the sleeve wall.
 31. A shot tube for the introduction of molten metal into a die cavity, wherein the tube is comprised of: a) a casing having a first end, a second end and a bore extending therethrough, wherein the first end is adapted to be connected to the die cavity; b) a sleeve protruding from the second end of the casing, wherein the sleeve has a pour opening for the introduction of molten metal; c) wherein the sleeve begins at a location proximate to the second end of the casing and extends away from the casing; and d) wherein the sleeve is made of a material from the group consisting of ceramic and cemented carbide while the casing is made of steel. 